Munge a copy of app.yaml instead of the original.
Munge a copy of app.yaml instead of the original.

Previously, the build edited the resources/app.yaml in the source tree,
resulting in unexpected git diffs in the event of a tele build failure.
Now, the build avoids this by making a copy of the entire resources
directory within the build dir and editing/building from that copy.

gravitational/stolon-app,gravitational/stolon-app